President Bush today called on the United Nations to hold Syria and its leaders accountable for "their continuing support of terrorism" and possible involvement in the assassination of former Lebanese prime minister Rafiq Hariri.

Addressing military officers' wives at Bolling Air Force Base in Washington, Bush also hailed official Iraqi certification today of the passage of a new constitution, saying that "Iraqis are making inspiring progress toward building a democracy" in the face of violence from Islamic extremists.

He called for continued sacrifice in Iraq and in the war on terrorism, calling Muslim radicals "enemies of humanity" who are pursuing "totalitarian aims" and who harbor "endless ambitions of imperial domination." He reiterated his earlier commitment to "never back down, never give in and never accept anything less than complete victory."

While much of his speech today essentially repeated an address he gave Oct. 6 in Washington on the war on terrorism, his comments on Syria appeared to be his toughest to date on that country and came in the wake of a U.N. investigative report that implicates Syrian officials in the Feb. 14 murder of Hariri in Beirut.

Saying that the United States is "determined to deny radical groups the support and sanctuary of outlaw regimes," Bush pointed to Syria and Iran, which he described as "state sponsors" of terrorism. He said countries such as Syria and Iran "have a long history of collaboration with terrorists, and they deserve no patience from the victims of terror."

This week, the U.N. Security Council "will hear a new report from an independent commission that points to Syrian involvement in the terrorist bombing that killed former Lebanese prime minister Hariri and 22 others last February," Bush said. "Syria is destabilizing Lebanon, permitting terrorists to use its territory to reach Iraq and giving safe harbor to Palestinian terror groups."

Noting that the United Nations has passed strong antiterrorism resolutions, Bush said, "Now the United Nations must act, and Syria and its leaders must be held accountable for their continuing support of terrorism, including any involvement in the murder of prime minister Hariri."

Syria has denied involvement in the crime and criticized the report issued last week by chief U.N. investigator Detlev Mehlis of Germany, who said the decision to assassinate Hariri could not have been taken without the approval of top Syrian security officials.

In an interview on CNN today, Imad Moustapha, the Syrian ambassador to the United States, repeated Syrian denials.

"Blaming Syria is very easy because it offers advantages to our political adversaries in Lebanon on one hand, and it allows the United States administration to continue its ongoing political campaign against Syria," Moustapha said. "President Bashar Assad has said that Syria would never, ever participate in such a terrible crime."

The ambassador also denied the Mehlis report's charge that Syria has not cooperated with the investigation, saying it was in his country's interest to "reveal the truth about the assassination" of Hariri and asserting that Syria was "more damaged by this crime than any other party in the whole Middle East."

In his speech today to the annual Joint Armed Forces Officers' Wives' Luncheon, Bush hailed Iraqi progress in maintaining security and building democracy. The new constitution that was put to a national referendum Oct. 15 "guarantees fundamental freedoms and lays the foundation for lasting democracy," he said.

Bush noted that "many more" Sunni Muslims voted in the referendum than in the general elections held in January, and he said the "level of violence was dramatically lower."

But he added, "We got more work to do, and it involves great risks for Iraqis and for American and coalition forces. The time of war is a time for sacrifice. And the greatest burden falls on our military families."

Bush acknowledged that "we've lost some of our nation's finest men and women in the war on terror" and said that "each loss of life is heartbreaking." But he added that "the best way to honor the sacrifice of our fallen troops is to complete the mission and lay the foundation of peace by spreading freedom."

He told the military spouses, "All of you also understand that sacrifice is essential to winning war. And this war will require more sacrifice, more time and more resolve."

While much of Bush's language in today's speech was identical to that in his Oct. 6 address to the National Endowment for Democracy, he dropped some of his earlier specifics from a passage on successes in foiling terrorist plots.

In his speech today, Bush said, "Together with our coalition partners, we've disrupted a number of serious al Qaeda terrorist plots" since Sept. 11, 2001, "including several al Qaeda plots to attack inside the United States."

In his earlier speech, Bush specified that "at least 10 serious al Qaeda terrorist plots" have been disrupted since the Sept. 11 attacks by Osama bin Laden's network, "including three" in the United States. He said authorities have "stopped at least five more al Qaeda efforts to case targets in the United States or infiltrate operatives into our country."

A White House list of the plots subsequently drew criticism from counterterrorism experts, who expressed puzzlement about why some incidents were listed and others were not. Intelligence officials said the White House overstated the gravity of the plots by saying they had been foiled, when most were far from ready to be carried out, Washington Post staff writer Sara Kehaulani Goo reported.